You have a PM (image of three days BQM, which folk can see if they go via camieabz.co.uk).
In the early hours of Thursday morning, we had terrific thunderstorms, and after one power cut, I decided to unplug all my PC / BB kit and wait it out (the big red bit).
As you can see, the latency rose due to the exchange interpreting it all as bad, so reducing speed (sync is always high, but profile and throughout suffers).
Then at 4am this morning, the latency dropped, so I assume a gateway reset or summat. So at least you know that latency can go down as well as up.